Balloon catheters are used for several medical procedures, including balloon angioplasty and stent delivery. The balloon may be inflated by an inflation device in the general form of a syringe assembly, and in general it is advantageous for the device to be capable of providing rapid inflation or deflation of the balloon while also providing fine adjustment of the balloon pressure. In addition, it is advantageous for the inflation device to maintain the balloon at a desired pressure without force being applied continuously by the operator.
Several inflation devices of the syringe design have been proposed which enable the piston of the syringe to move with respect to the barrel in both a freely reciprocating mode and a threaded or locked mode, for example U.S. Pat. No. 5,137,514 to Ryan and U.S. Pat. No. 5,147,300 to Robinson et al. A device such as described in these patents includes a thread engagement mechanism that may lock the piston into a threaded mode. However, in each case the operator is required to either depress a trigger or move a control button before the thread engagement mechanism is released.